tests: Add fuzzing harness for HTTPRequest, libevent's evhttp and related functions

Summary:

Add fuzzing harness for HTTPRequest, libevent's evhttp and related
functions.

Backport of core PR18363.

Test Plan:

ninja bitcoin-fuzzers
./src/test/fuzz/http_request <path__to_corpus>

This should crash fairly quickly, the fix will be part of another diff.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D9000